Improvement of J_c by cold high pressure densification of binary, 18-filament insitu MgB_2 wires

摘要

Cold high pressure densification (CHPD) has recently been found to be a promising way to improve the critical current density, J_c, in single-core MgB_2 wires prepared by insitu processing. In this work, the CHPD process was also applied to multifilamentary, binary MgB_2 wires, leading again to a strong enhancement of the transport J_c. The fields and where the transport J_c at 4.2K reaches the value 1 × 104Acm- 2 for parallel and perpendicular fields were determined as 8.5 and 8.2T, respectively (0.1 νVcm~(- 1) criterion). The behaviour of J_c versus B at 20 and 25K was almost isotropic, the corresponding values being 4.7 and 3T, respectively. The observed enhancement of J_c by a factor 2.3 at 4.2K at all applied fields up to 10T in densified samples is directly correlated with the observed enhancement of the mass density and microhardness. The decrease of the electrical resistivity of the densified wire reflects improved grain connectivity in the filaments. The improvement of J_c by CHPD was still observed after sequential pressing with overlapping regions, up to a total wire length of 150mm. This result is promising as regards practical applications.